This invention relates to internal structures, often referred to as "liquid distributors", that are used in vessels employed in chemical plant and oil refineries for mass transfer and heat transfer applications such as distillation, fractionation, absorption, scrubbing, contacting, stripping and quenching.
In such towers the liquid is typically caused to flow down the tower so as to be contacted with vapors flowing counter-current up the tower. This contact tower can often have a plurality of segments, each comprising a distributor system and packing, located sequentially in the same tower.
It is frequently advantageous that the liquid flow in such segments is in thin film fashion so as to maximize the degree and time of contact with the liquid. This can be accomplished for example by providing that the segments comprise structured or random packing elements over which the liquid streams leaving the distributor pass in thin film flow fashion. Other methods of bringing about the contact are known in the art.
All these methods result in liquid arriving at the bottom of the segment of the tower containing such contacting structures where it needs to be collected. Typically this is done by a series of collector devices which then channel liquid to distributor conduits from which it may again be passed down the next lower segment of the mass transfer tower. Similar distribution structures are located at the top of the towers at the point at which the liquid is introduced.
In each case it is important that the liquid be evenly distributed throughout the cross-section of the tower so as to maximize the vapor/liquid contact potential created by the packing elements and to prevent uneven treatment of the liquid and/or vapor passing through the device. To this end the distribution structures usually comprise distributor conduits, such as troughs, feeding branch conduits which themselves have apertures in the walls through which a flow of liquid can be directed to the top levels of the packing.
It would obviously be possible to multiply the number of apertures in the branch trough walls to enhance the development of complete and expeditious wetting of the packing elements in an overall uniform manner. This would however mean that the apertures would need to be relatively small to ensure that each received an equal amount of liquid for distribution. Unfortunately small holes are more subject to obstruction by solid impurities in the liquid flow and this results in exactly the uneven flow that is to be avoided.
It is well-known to attack this problem by using relatively fewer holes that are bigger and using devices for spreading out the flow from each hole such that it reaches the packing as a plurality of drips. This is done by contacting the liquid flow exiting horizontally from each aperture with a vertical surface that spreads the flow and terminates in a plurality of drip edges or points that contact the top surfaces of the packing. Suitable devices are described for example in U.S. Pat. Nos. 4,264,538; 4,816,191; and 4,855,089. Such devices typically place a spreader plate opposite the aperture in the conduit wall such that the exiting liquid hits the plate and is spread in a relatively thin flow which then passes to drip edges or fingers. This approach can have drawbacks in that the location of the plate necessarily limits the proximity of adjacent conduits. In addition a partially blocked aperture could reduce the flow to the extent that the liquid flow would not even reach the plate. Also if the flow is particularly strong the position of the plate may have to be adjusted to avoid splashing or guards provided to ensure that the flow is channeled in the desired direction.
In another device marketed commercially by Hydronyl Ltd in the United Kingdom in the early 1970's a liquid flow was distributed by closed conduits with a plurality of apertures at opposite ends of a horizontal diameter or chord set at an appropriate depth. The liquid in the conduit exited through the holes and into contact with a vertical sheet metal spreader plate with a lower portion that conducted the liquid film formed on the plate to a vertical perforated plate directly below the pipe such that the liquid ran down both sides of the perforated plate. In a preferred form the vertical perforated plate then contacted a similar vertical perforated plate set at right angles to the first. This acted to spread a portion of the liquid at right angles to the rest of the flow and thereby enhance the uniformity of distribution across the packing to which the down-flowing liquid was ultimately fed. This arrangement worked well but was subject to many of the problems discussed above.
In yet another prior art system the conduit has the form of a deck provided with risers through which gas can flow upwards and a plurality of holes through which down-flowing liquid can pass. This eliminates the spacing problem but delivers the liquid in streams rather than from drip points which are more effective in promoting uniform flow through the system.
The present invention provides a novel and advantageous alternative to such devices. It has the advantage of permitting the use of relatively large holes that would minimize blocking while at the same time permitting very wide and even distribution of the flow under a wide range of flow conditions.